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Solar Thermal Cooling GLOBAL SOLAR Solar Heating and Cooling WATER HEATING application factsheet PROJECT Project partners: Solar thermal cooling APPLICATION: PRINCIPLES AND BASIC OPERATION Thermally driven cooling The main feature of a solar cooling system, beyond the solar collec- SYSTEM REQUIREMENTS using solar thermal collectors tor field, is the thermally driven chiller. On the thermal supply side, the solar thermal system is rather conventional, consisting of high Temperature (small-scale and large-scale) quality solar collectors, a storage tank, a control unit and pipes. 6°C to 20°C (cooling) Average cooling temperature For the cooling process, the main element is the thermally range. The temperature DESCRIPTION OF USE driven cooling machine but the process of heat rejection is also The demand for cooling may be driven by required from the solar important. This means that cooling towers or other heat rejection thermal plant changes different aspects, comfort and refrigeration solutions are required. according to needs and being the most common uses. In fact, the desired performance. cooling demand is growing worldwide, even It can start at 80 °C but The most common technological solution is an absorption some systems operate well in colder climates, as comfort demand rises. cycle: the heat is used to chemically “compress” the refrigerant above 150 °C. This results in an increase in air conditioning by desorbing (separating) it from a sorbent, cooling is produced mainly for tertiary buildings but also for as the “compressed” liquid is expanded in the evaporator to residential applications. Refrigeration is Advanced Remote Advanced turn into gas. Metering Monitoring Controls increasing as well with a wider variety of use, mainly within the food industry. Air conditioning is the main process used for comfort cooling. It involves changing Solar heat air properties, such as lowering temperature and humidity levels. Refrigeration implies Solar cooling systems are complex bringing temperature to low levels, even systems that require advanced metering below freezing point. and advanced controls. Remote monitoring Chilled Water is a great advantage in such systems. Thermally-Driven Cooling is basically achieved by retrieving Cooling Process heat from a fluid or gas and transferring it Operation & Maintenance to the environment, which is usually called heat rejection. This transfer can be done mechanically or chemically. One of the technologies used for cooling Conditioned Air High purposes are thermally driven chillers. Solar cooling systems require high operation These use thermal energy to cool down gases & maintenance compared with a regular solar or fluids. This thermal energy can be provided thermal system providing domestic hot water. Expert support is required, with pre-planned by different technologies, including solar maintenance visits. thermal energy. SECTORS COVERED EXAMPLES OF APPLICATIONS More generally, there are two main commercially available solar Solar cooling is suitable for residential, cooling processes: Residential commercial, institutional and industrial • Closed cycles, where thermally driven absorption or 3 Single-family house use. The solar cooling supply is equal adsorption chillers produce chilled water for use in space to the demand: when the sun is at its hottest conditioning equipment. 3 Multi-family house solar irradiation is high, the maximum energy • Open cycles, which typically use water as the refrigerant Tertiary is available and the demand is also high. and a desiccant as the sorbent for direct treatment of air 3 Commercial A typical solar cooling system also in a ventilation system. (offices, hotels, shopping centers, …) provides space heating and hot water, 3 Institutional besides cooling. One of the main require- Generally, solar cooling systems are not installed without backup (schools, nursing homes, hospitals, …) ments of such systems is to have an effective for cooling and heating. Therefore the majority of the financial heat rejection system. This means that savings are on the avoided energy use, rather than on the avoided Industrial applications requiring both heating and cooling traditional cooling device cost. 3 Low temperature processes (washing, dyeing, pasteurization, …) are rather well suited for this technology (for instance, dairy farms, hotels or residential houses with heated swimming pool). WORLDWIDE APPLICABILITY This technology is particularly suited for sunny and dry climates. Nevertheless, it can be applied in other climates, as solar thermal energy can be used for air conditioning in the summer, having a perfect correlation between the increase in comfort cooling demand in summer and the availability of the solar resource. As an example, in 2014, out of the 1200 systems of all technology types and sizes accounted for worldwide (mostly between 10 and 35 kW cooling capacity), more than 75% were installed in Europe. From an energy system point of view, it should be taken into account that solar cooling can significantly reduce the electricity demand. Below 1000 cooling degree-days/year This is particularly relevant in countries with a warmer climate and/or having Between 1000 and 2000 cooling degree-days/year problems managing peak loads in summer due to rising cooling demand Over 2000 cooling degree-days/year as well as high fossil fuel and electricity energy costs. Map of Worldwide Cooling Needs BENEFITS The benefits of solar cooling systems cover several These factors depend on the location (affecting In terms of energy costs, solar cooling can range aspects: environmental, political and economic. climate, insulation, taxes, cost of living, etc.) from 140 to 365 USD/MWhth (126 to 328.5 EUR/ (1) and quality of the system (affecting performance, MWhth) . Prices, excluding installation cost and Environmental benefits stem from the capacity lifetime and cost). This can vary significantly from distribution system to the building for the package to reduce harmful emissions. The reduction country to country. solutions, dropped from about 6000 EUR/kW of CO2 emissions depends on the quantity of (6666 USD/kW) in 2007 to about 4500 EUR/kW fossil fuels replaced directly or indirectly, when Therefore, average investment costs for solar (in 5000 USD/kW) 2013 (2). the system replaces the use of carbon-based cooling systems can vary greatly from country electricity used for water heating. The savings will to country and between different systems. be greater if the system provides both cooling and According to the IEA, the investment costs heating, when not operating for cooling or eventu- of solar cooling can range from 1600 to ally using the residual heat from the heat rejection. 3200 USD/kWth (1440 to EUR/2880 kWth). Political and economic benefits are associated with the potential savings in energy costs Range of Range of and the possibility of improving energy security, gas costs electricity costs by reducing energy imports, while creating local Solar cooling jobs related to the manufacturing, commercializa- tion, installation and maintenance of solar cooling Large scale systems southern United States systems. Large scale systems Europe Regarding the energy costs, and potential savings, Solar hot water China (thermosiphon) there are three main aspects to consider that Solar hot water northern Europe (forced circulation) have a bigger impact on the comparable costs Solar hot water central Europe (forced circulation) of the energy produced by a solar thermal system. Solar hot water southern Europe (thermosiphon) These are the initial cost of the system, the lifetime 0 50 100 150 200 250 300 350 400 of the system and the system performance. Costs of solar heating and cooling (USD/MWhth), Source: IEA 2012 EXAMPLES AFRICA AMERICA EUROPE Telecommunications company in North High School in Arizona, USA Office Building in Kordin, Malta Johannesburg, South Africa This is a warm environment with temperatures In 2008, this office building in Kordin, In 2014, a concentrating solar cooling system often soaring above 40 °C that has important Malta was equipped with a solar cooling was installed in Johannesburg, South Africa, cooling requirements. Therefore, it is not system made up from 30.5 m² of flat comprising 242 sun-tracking solar mirrors surprising that the 1.75 MWth solar cooling plate collectors and 7 m² of vacuum covering 484 m2. The mirrors move into system installed in the Desert Mountain tube collectors. With a capacity over a self-cleaning position when it rains, and High School in Arizona, USA, is one of the 26kWth, the system generates 10 kWth turn down into a protective stow position most powerful solar cooling systems in of cold in a chiller consisting ammonia on cloudy days. This system is used by a operation worldwide. The system is served and water. The cold water is stored telecommunications company to cool the by a solar thermal plant with a capacity of in a 200 l tank, while the hot water IT equipment. The collector field provides 3.4 MWth (4 865 m²) and was installed in storage tank is 400 l. The distribution a two-stage absorption refrigerator with 2014. This system provides solar thermal air is done by fan coils and floor cooling. pressurized water at a temperature of 180 °C, conditioning for the school. It covers 30% of providing an annual gross heat production the annual cooling demand and 100% during of 391 MWh. The system has a peak the summer when the school is seldom used. cooling capacity of 330 kilowatts. 18 Reference: Reference: Reference: www.htxt.co.za/2014/07/09/using- www.solid.at/images/pdf/ref_e_DMHS.pdf www.solarnext.eu/eng/ref/coolingkitprojects.shtml solar-energy-to-power-mtns-air-conditioning/ Key data Key data Key data 2009 4 peak cooling capacity of 330 kilowatts Cooling 1.75MWth 30% performance pressurized Solar collector hot water at solar cooling capacity 242 system 10kW sun-tracking 180 °C of the annual 26kWth solar mirrors gross heat cooling demand covering production of 2 Using both flat plate 484m 2 391 MWh 3.4 MWth (4865m ) solar plant and vacuum tube collectors REFERENCES (1) Values based on the Technology Roadmap: Solar Heating and Cooling, IEA 2012.
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